Dinosaurs are a diverse group of animals that were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period (about 230 million years ago) until the end of the Cretaceous (about 65 million years ago), when the Cretaceous-Paleogene extinction event led to the extinction of most dinosaur species at the close of the Mesozoic era. The fossil record indicates that birds evolved within theropod dinosaurs during...